content: /**
   * Copyright (c) 2016-present, RxJava Contributors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
   * compliance with the License. You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software distributed under the License is
   * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
   * the License for the specific language governing permissions and limitations under the License.
   */
  package io.reactivex.observable.extensions;
  
  import java.util.concurrent.Callable;
  
  /**
   * A marker interface indicating that a scalar, constant value
   * is held by the implementing reactive type which can be
   * safely extracted during assembly time can be used for
   * optimization.
   * <p>
   * Implementors of {@link #call()} should not throw any exception.
   * <p>
   * Design note: the interface extends {@link Callable} because if a scalar
   * is safe to extract during assembly time, it is also safe to extract at
   * subscription time or later. This allows optimizations to deal with such
   * single-element sources uniformly.
   * <p>
   * @param <T> the scalar value type held by the implementing reactive type
   */
  public interface ScalarCallable<T> extends Callable<T> {
  
      // overridden to remove the throws Exception
      @Override
      T call();
  }
  